2012 GMC Canyon Owner's Manual - Page 284

10-48 Vehicle Care (C) Aspect Ratio: A two‐digit number that indicates the tire height‐to‐width measurements. For example, if the tire size aspect ratio is 60, as shown in item C of the illustration, it would mean that the tire's sidewall is 60 percent as high as it is wide. (D) Construction Code: A letter code is used to indicate the type of ply construction in the tire. The letter R means radial ply construction; the letter D means diagonal or bias ply construction; and the letter B means belted‐bias ply construction. (E) Rim Diameter : Diameter of the wheel in inches. (F) Service Description: These characters represent the load index and speed rating of the tire. The load index represents the load carrying capacity a tire is certified to carry. The speed rating is the maximum speed a tire is certified to carry a load. Tire Designations Tire Size The following is an example of a typical passenger vehicle tire size. Tire Terminology and Definitions Air Pressure: The amount of air inside the tire pressing outward on each square inch of the tire. Air pressure is expressed in kPa (kilopascal) or psi (pounds per square inch). Accessory Weight: The combined weight of optional accessories. Some examples of optional accessories are automatic transmission, power steering, power brakes, power windows, power seats, and air conditioning. Aspect Ratio: The relationship of a tire's height to its width. (A) Passenger (P‐Metric) Tire: The United States version of a metric tire sizing system. The letter P as the first character in the tire size means a passenger vehicle tire engineered to standards set by the U.S. Tire and Rim Association. (B) Tire Width: The three‐digit number indicates the tire section width in millimeters from sidewall to sidewall.